At first, it might be that using a utility to generate a custom image to flash using pwnagetool is what people do at first, so the iOS 5 rev is pre-jailbroken.
However, for those with this year's iPhone, it will be waiting a few months before a JB is available. It might be a few months, it may be longer. Apple is getting better at the lockdown game, and has bested everyone for almost nine months now with the baseband update. Hopefully a JB isn't going to take this long.